Monorail bogies are known in the art, and are used in many monorail car assemblies. However, a common deficiency with monorail bogies, and particularly straddle beam monorail bogies, is that they have a tendency to roll from side-to-side when traveling on a monorail track, thus causing the monorail car to sway from side-to-side. This rolling motion can be concerning for passengers, and in some cases can even be dangerous.
In order to help prevent rolling effects, existing monorail bogies have included stabilizing wheels that are positioned centrally with respect to the upper guiding wheels, but are positioned lower on the monorail track than the upper guiding wheels. Unfortunately, this type of arrangement creates chording effects when the monorail car travels through curves in the track, which in turn causes undesirable bogie roll. More specifically, as the monorail car travels through curves in the track, the upper guide tires are positioned by the chord of the curvature while the lower stabilizing wheel is at the midpoint of the chord, thereby resulting in an offset and undesirable roll of the bogie.
FIG. 1 shows a top plan view of a prior art bogie arrangement, wherein the prior art bogie 4 includes four upper guide tires 6 and two lower guide tires 8. When the prior art bogie 4 travels on straight sections of track, all of the tires 6 and 8 are in alignment. However, when the prior art bogie 4 travels around a bend in a curve, the upper guide tires 6 are positioned on the outside of the chord, such that they can be joined by a straight line, whereas the lower guide tires 8 are positioned within the center of the chord. As such, the lower guide tires 8 are not in alignment with the four upper guide tires 4, which creates an offset. This offset creates an imbalance in the railcar, which results in roll about the track.
In light of the above, it can be seen that there is a need in the industry for an improved monorail bogie that alleviates, at least in part, the deficiencies of the prior art, and improves on the overall roll behavior of the monorail bogie particularly in curves or curve transitions.